Originally Posted by GammaWill  Mike, the brushless motors I'm looking at have metal cases. That should help with the heat dissipation I hope. As for driving them, the controllers expect a .5ms to 1.5ms width signal to vary their speed. 10 years ago, I happened to have built servo driver using a 555 timer to generate the pulsewidths. It drove a servo just fine, and should drive the hobby-type brushless ESCs. What would be really cool is to get MACH3 to output a variable voltage that I could use to drive the ESC. A simple PIC (even a puny 16F84) could handle the voltage-to-PWM conversion for me. I'll look into it and report back when I have some results.
Chris, thanks for the tip. I looked into the Proxon, first, and realized it was overkill for my needs. I'll be using the high-speed Wolfgang spindle to cut very small cavities in aluminum. No cavity is over 1/4" deep or over 1.5" in length. With an ultra-small stepover and stepdown of .00625", it should be hardly any stress on the cutter. I don't think a 1/32" cutter could handle much stress any way. I've heard those little babies snap off and go flying across the room at the slightest abuse. I'll definitely have an enclosure around my mill when it is whirring away at 40K RPM with a tiny cutter in the collet! 
As for load on the bearings, the motor drives the spindle, so I'm not expecting any undo stress on the motor bearings. If the brushless motor shaft were the spindle, then I'd be in real trouble, wouldn't I!
Regarding torque, I wonder how I can calculate that? Does anyone know how I might determine the torque on a 1/32" 2-flute end mill running at 40K RPM, cutting .00625" into 6061-T6 aluminum at 10 IPM? I suspect it is negligible at that rate. |
Thats not torque thats side load, torque is what the motor produces. Its most often referenced to horsepower but can also be used to refer to holding power of a servo/stepper. The rest is your feed rate, which really has nothing to do with torque. In which case your figuring chip load per flute and thats going to be very very small(at 12800 rpm give or take). I am not familiar with wolfgang spinldes, so my assumption is that it fairly small, and you have to attach the motor to the input of it directly(via a coupling of some sort). I know enough about about the hobby motors to tell you that they will not last much more then a half an hour at speed or they will burn up, even under forced air flow cooling(don't forget in an airplane its forcing air over the motor). I really think your best bet will be something along the lines of Proxxon or an air spindle. I dabbled in RC aircraft I know that the fellows that were teaching me did not like the electrics because they required a cooling down period.
chris